Trimble Outdoors SK8 - Manual (Page 202)

Glossary-4 Lassen-SK8 Embedded GPS Module
Glossary
elevation mask angle A measure of the minimum elevation angle, above the horizon, above
which a GPS satellite must be located before the signals from the satellite
will be used to compute a GPS location solution. Satellites below the
elevation angle are considered unusable. The elevation mask angle is
used to prevent the GPS receiver from computing position solutions
using satellites which are likely to be obscured by buildings or
mountains.
ellipsoid In geodesy, unless otherwise specified, a mathematical figure formed by
revolving an ellipse about its minor axis. It is often used interchangeably
with spheroid. Two quantities define an ellipsoid; these are usually given
as the length of the semimajor axis, a, and the flattening, f = (a - b)/a,
where b is the length of the semiminor axis.
ephemeris A set of parameters that describe the satellite orbit very accurately. It is
used by the receiver to compute the position of the satellite. This
information is broadcast by the satellites.
epoch Measurement interval or data frequency, as in making observations every
15 seconds. Loading data using 30-second epochs means loading every
other measurement.
firmware A set of software computer/processor instructions that are permanently
or semi-permanently resident in read-only memory.
frequency The number of vibrations per second of an audio or radio signal.
Measured in hertz (Hz), kilohertz (kHz), or megahertz (MHz).
GPS frequencies are: L1 = 1575.42 MHz
L2 = 1227.60 MHz
GDOP Geometric Dilution of Precision. GDOP describes how much an
uncertainty in pseudo-range and time affects the uncertainty in a position
solution. GDOP depends on where the satellites are relative to the GPS
receiver and on GPS clock offsets.
geodetic datum A mathematical model designed to best fit part or all of the geoid. It is
defined by an ellipsoid and the relationship between the ellipsoid and a
point on the topographic surface established as the origin of datum. This
relationship can be defined by six quantities, generally (but not
necessarily) the geodetic latitude, longitude, and the height of the origin,
the two components of the deflection of the vertical at the origin, and the
geodetic azimuth of a line from the origin to some other point. The GPS
uses WGS-84.
geoid The actual physical shape of the earth which is hard to describe
mathematically because of the local surface irregularities and sea-land
variations. In geodetic terms it is the particular equipotential surface
which coincides with mean sea level, and which may be imagined to
extend through the continents. This surface is everywhere perpendicular
to the force of gravity.
2-D Two Dimensional. A 2-D position is defined as latitude and longitude.
Altitude is assumed to be fixed.